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Hi,
I've been playing with spaces of modular symbols over finite fields, and
I ran into two issues that seem to be separate (they're tickets #1231
and #1232 now):
1. doing
ModularSymbols(1,8,0,GF(3)).simple_factors()
gives
- ------------------------------------------------------------
Unhandled SIGSEGV: A segmentation fault occured in SAGE.
This probably occured because a *compiled* component
of SAGE has a bug in it (typically accessing invalid memory)
or is not properly wrapped with _sig_on, _sig_off.
You might want to run SAGE under gdb with 'sage -gdb' to debug this.
SAGE will now terminate (sorry).
- ------------------------------------------------------------
The same phenomenon occurs over other finite fields.
2. doing
ModularSymbols(1,6,0,GF(2)).simple_factors()
gives
-
---------------------------------------------------------------------------
<type 'exceptions.AssertionError'> Traceback (most recent call last)
/home/ghitza/sage/<ipython console> in <module>()
/opt/sage/local/lib/python2.5/site-packages/sage/modular/modsym/space.py
in simple_factors(self)
996 ASSUMPTION: self is a module over the anemic Hecke algebra.
997 """
- --> 998 return [S for S,_ in self.factorization()]
999
1000 def star_eigenvalues(self):
/opt/sage/local/lib/python2.5/site-packages/sage/modular/modsym/ambient.py
in factorization(self)
1064 D = sage.structure.all.Factorization(D, cr=True)
1065 assert r == s, "bug in factorization -- self has
dimension %s, but sum of dimensions of factors is %s\n%s"%(
- -> 1066 r, s, D)
1067 self._factorization = D
1068 return self._factorization
<type 'exceptions.AssertionError'>: bug in factorization -- self has
dimension 2, but sum of dimensions of factors is 3
(Modular Symbols subspace of dimension 1 of Modular Symbols space of
dimension 2 for Gamma_0(1) of weight 6 with sign 0 over Finite Field of
size 2) *
(Modular Symbols subspace of dimension 1 of Modular Symbols space of
dimension 2 for Gamma_0(1) of weight 6 with sign 0 over Finite Field of
size 2) *
(Modular Symbols subspace of dimension 1 of Modular Symbols space of
dimension 2 for Gamma_0(1) of weight 6 with sign 0 over Finite Field of
size 2)
- -------------------------------------------------------------------------
I have not looked at the implementation, but as far as I know the
algorithms with modular symbols work directly over the field of
definition, so it seems unlikely that this is related to the problem
that Ifti raised a few days ago, about reduction of coefficients modulo
prime ideals.
Best,
Alex
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